Writing new C++ code with all the modern approaches and tooling doesn't sound so bad. Troubleshooting a big legacy C++ codebase is probably something that Dante would have included in his Inferno as a punishment for pride and hubris.
A modern project should be able to use most of C++17 at least. Even if you still need to target some ancient garbage like Windows XP, you can use an MSVC toolchain that supports C++17. That's a good basis to work from.
So your real concern is the moldy old code that's written for C++03, that's still not using std::unique_ptr or anything equivalent. If you're given license to finally rewrite that code to modern standards, that can be fun if it's not a complete mess. But if you just have to live with it, and still write C++03, absolutely not, I would never do that job.